The Big Bang

[kwicky]

I can't get my head around the looking back into space from the Hubble Telescope and seeing events that took place 12 billion years ago. How does this work?

[Bmw-Rider]

Universal studios Hollywood, Planet Saturn.

[TeeGee]

What we see now, via Hubble, is what was happening when the light we see was transmitted. If the object we are looking at is 12 billion light years away then what we see now happened then. The object may not still be there !

[fo3nix]

Imagine you're at a football ground, and you're watching a free kick about to be taken.

What you're watching is something that's happened in the past -- you're looking back in time!

This is because the footballer goes to kick the ball. Any photons from lights or the sun hit him and bounce off in all directions, and then travel to your eyes, which is how you see him. However, it's taken some time for the light to travel from the footballer to you, so what you're seeing is what happened a very small fraction of time in the past.

The only reason you don't notice any of this is because light moves so fast -- 300 million metres every second. So you're only seeing a very, very small amount of time in the past.

Hubble telescope is exactly the same. It's just a big eye, looking into space at some event or object, as you were at the football ground. The difference is that it's looking at things very, very far away, so the light actually takes a noticeable amount of time to travel from the object to Hubble. Hence, it's still looking back in time as you were at the football ground, just further in time than you were.

[Phantaxus]

it takes 8 minutes for the light from the sun to reach earth. so if you had access to some sort of celestial light switch and you turned it off you would have to wait to see the results.

[ryepie]

Just to nitpick (after all this IS AnswerBank, nitpicking central), if you had a celestial lightswitch, and used it to turn off the sun (i.e. cease it's nuclear reactions), then you'd have to wait 1000s of years to see it 'go out' due to the average travel time of photons from the core to the surface.

[kwicky]

I think I can see the analogy with the footballer. But moving this on more free kicks would be taken so obliterating the earlier free kick. Does this mean that after the big bang no event took place to obscure the past?

[fo3nix]

You mean, why hasn't the light been blocked by something else?

If so, it has, a great deal of it. It's just that there's still some that ends up at us, from some parts of the universe a long way away.

[mibn2cweus]

The following link is somewhat dated (1995) but offers some relevant background on how the age and size of the visible universe is conceived. . .

Cosmological yardsticks

[Phantaxus]

ryepie : i didnt say how long you would have to wait